The present invention relates to nuclear fuel assemblies, and in particular to an apparatus for the determination of radiation induced growth of a nuclear fuel assembly in a nuclear reactor.
Nuclear reactors need to be periodically maintained and inspected as well as refueled. Refueling operations involve the removal of the equipment and apparatus positioned in the reactor vessel above the reactor core which comprises nuclear fuel assemblies each of which contain nuclear fuel rods held or supported in parallel positions by spacers and an upper and a lower tie plate. The nuclear fuel assemblies are supported in the reactor core by a lower core support plate and extend upwards to an upper core support plate which serves to align the upper portion of the fuel assemblies which are positioned at their lower ends in predetermined positions in the lower core support plate so that the fuel assemblies are parallel to one another. The upper tie plate of the assemblies contain suppression springs to ensure that the assembly is firmly seated on the lower core support plate at all times.
The distance between the top of the solid portion of the upper tie plate along its span of a nuclear fuel assembly and the underside of the upper core support plate of the reactor determines the available room for radiation induced growth of the assembly due to reactor operations.
Current methods of determining nuclear fuel assembly length and growth, and assessing the available space for growth after the tie plate suppressions springs of the fuel assembly contact and are compressed a given amount against the underside of the upper core support plate require measurements and calculations which are complex and may lead to significant uncertainties. There aren""t any known current means to measure the upper tie plate to core plate gap directly.
It would therefore be an advantage over the prior art designs to provide an apparatus for determining the gap between the upper tie plate and upper core support plate and therefore the determination of the fuel assembly growth resulting from radiation induced growth.
In accordance with one embodiment of the present invention, a radiation induced growth indication apparatus is provided for the determination of radiation induced growth of a pressurized water reactor nuclear fuel assembly positioned in a reactor core having an upper core support plate, the nuclear fuel assembly including an upper tie plate, comprising an inelastically compressible structural member disposed between the upper tie plate and upper core support plate and secured to a top of the upper tie plate and extending into contact with the upper core support plate for compression due to the movement of the fuel assembly against the upper core support plate as a result of radiation induced growth.
In accordance with another embodiment of the present invention, a radiation induced growth indication apparatus is provided for the determination of radiation induced growth of a pressurized water reactor nuclear fuel assembly positioned in a reactor core having an upper core support plate, the nuclear fuel assembly including an upper tie plate, comprising a rod disposed between the upper tie plate and upper core support plate and positioned at a proximate end in an aperture formed into a top of the upper tie plate and a distal end of the rod extending into contact with the upper core support plate for compressing the distal end further into the aperture due to the movement of the fuel assembly against the upper core support plate as a result of radiation induced growth.